Process for deoxidizing iron and steel



Patented Jan. 31, 1950 PROCESS FOR DEOXIDIZING IRON AND STEEL James C.Vignos, Canton, Ohio, assignor to Ohio Ferro Alloys Corporation, Canton,

poration of Ohio Ohio, a cor- No Drawing. Application June 27, 1946,Serial No. 679,865

2 Claims.

The invention relates to improvements in the manufacture of iron andsteel and particularly to that part of the process known as blocking.

In the manufacture of killed steels, and where blocking of the heat inthe furnace is required, it is customary to stop the action of the bathby the addition of to l&% ferro-silicon. This addition of the 10% to 14%ferro-silicon sinks through the slag and into the molten metal below andgoes into solution thus efiecting deoxidation of the molten metal to apoint where the reaction between the carbon content and the FeO contentis stopped.

The amount of silicon added in this manner usually ranges from 06% todepending upon the degree of oxidation of the metal and the length oftime it is desired to block the same.

During the period in which the heat is thus blocked considerable silicais formed as a result of the oxidation of the silicon, and this silicaremains trapped, or in solution, in the molten metal resulting inobjectionable inclusions in the finished steel.

Another method employed in blocking steel or iron in the furnaceconsists in adding powdered 50% ferro-silicon to the slag when the bathhas reached the desired carbon content.

This method of deoxidation lowers the FeO content of the slag causingthe Foo to flow from the metal to the slag which lowers the FeO in thebath below the point where it will react with the carbon in the metal.

There are certain disadvantages inherent in the use of both of the abovemethods of blocking the heat in an effort to prevent or retard further ncarbon loss during the final step of the melt.

Where the 10% to 14% ferro-silicon addition is made to the bath theformation of undesirable inclusions cannot be prevented and in themethod where the powdered 50% ferro-silicon is added to the slag fordeoxidizing the same, it is difficult to prevent a phosphorous reversioninto the steel from the slag.

I have discovered that a much improved practice results, if instead ofdeoxidizing the steel, by making additions of 10% to 14% ferro-siliconthereto, or deoxidizing the slag by the addition of powdered 50%ferro-silicon to the slag, as above described, lumps of to 60%ferro-silicon are added to the molten bath of slag and metal so as to gointo solution immediately at the interface, thus effecting deoxidationat this point.

It is therefore an object of the invention to provide a much improvedpractice for deoxidizing or blocking iron or steel heats.

Another object is to provide a more economical method of effectivelyblocking the heat.

A further object is to provide a method of blocking the heat whichproduces a cleaner steel.

Still another object is to provide a method of blocking iron or steelheats by the addition of lumps of dense 30% to ferro-silicon.

A still further object of the invention is to provide such a methodwhich includes the addition of lumps of 30% to 60% ferro-silicon whichhave been treated with a wetting agent.

The above objects together with others which will be apparent from thefollowing description, or which may be later referred to, may beattained by carrying out the improved method in the manner hereinafterdescribed in detail.

In carrying out the improved method, when the heat of metal has reachedapproximately the desired carbon content, there is added to the moltenbath of slag and metal, lump 30% to 60% ferrosilicon which is preferablyin the form of lumps of 50% ferro-silicon one inch in thickness andlarger.

For this purpose I prefer to use dense ferrosilicon which is produced bycasting in metal molds as described in U. S. Patent No. 2,197,660 ofApril 16, 1940,'to H. V. Glunz. The 50% ferrosilicon as produced in thepast has been cast in sand beds producing a rather porous product.

The dense lump 30% to 60% ferro-silicon sinks through the slag to theinter-face between slag and metal, and I have further discovered that ifsand cast lump 30% to 60% ferro-silicon is coated with a wetting agentit will also readily sink through the slag to the inter-face.

Further I have found that by coating lumps of dense 30% to 60%ferro-silicon with a wetting agent, they will sink more readily throughthe slag.

A great variety of wetting agents are suitable for this purpose, such asthe group or products known as oxidants which are compounds havingavailable free oxygen such as sodium nitrate, sodium chlorate,peroxides, permanganates, etc. Another wetting agent suitable for thepurpose is a group of products containing halogens such as sodiumchloride, calcium fluoride, etc.

Still another group of suitable wetting agents are derived from thegroup of products consisting of reaction products of an acid with ametal, such as sulphates, chromates, borates, etc.

The lump 30% to 60% ferro-silicon, either dense or sand cast, may beeither immersed in, or sprayed with, a solution of the wetting agent soas to produce a film on the surface of the ferrosilicon.

This film allows the ferro-silicon lumps to become wet by the slagimmediately on addition to the furnace, and to sink through the slag tothe inter-face between slag and metal. Due to its specific gravity, andlow melting point, the lump 30% to 60% ferro-silicon goes in thesolution immediately at the inter-face, thus effecting deoxidation atthis point.

Since the deoxidation thus takes place at the upper layer of the metaland the lower layer of the slag, transfer of FeO from the slag to themetal is retarded to a greater extent than if the deoxidation took placeentirely in the slag or entirely in the metal.

The improved method of effecting deoxidation at the inter-face thusovercomes the objections inherent in the method of blocking the heat bythe use of to 14% ferro-silicon, or powdered 50% ferro-silicon in theslag. I

The silicates formed by reducing the iron oxides are formed close to theinter-face and are therefore absorbed by the slag producing a metal freefrom objectionable silicates.

Further, since the deoxidation is mainly at the inter-face and not inthe slag, there is no danger of phosphorous reversion from the slag tothe metal.

Shortly after the lump to 60% ferrosilicon is added to the inter-facebetween the slag and metal of the bath the final additions of alloyingelements or other deoxidizers may be made, and when these additions aremelted the heat may be tapped.

Although in using the lump dense 30% to 60% ferro-silicon for arrestingthe action of the iron oxide on the carbon in the metal, the wettingagent may be eliminated, and the invention can be successfully carriedout without first coating the ferro-silicon lumps with a wetting agent,I have found that the use of a wetting agent has certain advantages andthat when it is eliminated there is more deoxidation of the slag thanwhen it is used and therefore more possibility of a phosphorousreversion.

The proper amount of lump 30% to 60% ferro-silicon required foreffectively blocking the heat can be readily and accurately determinedby a few trial heats. For example, I have found that when a heat of250,000 pounds had reached a carbon content of .20 and an addition of.12% of contained silicon in the form of lump 50% ferro-silicon wasadded to the furnace in 300 pounds lots through the second and fourthdoors of the furnace, that in two or three minutes after the addition ofthe ferro-silicon the bath was effectively blocked and there were only afew occasional bubbles at the end of the bath. The

heat remained blocked for a total of twentyseven minutes before it wastapped.

From the above it will be evident that this method of deoxidationovercomes the disadvantages of prior practice and since the cheapestform of silicon available is that contained in 50% ferro-silicon, theprocess is more economical than prior practice.

I claim 1. In the manufacture of iron and steel, the method of blockingthe heat when it has reached the desired carbon content, which consistsin coating one inch and larger lump dense 50% ferro-silicon with thefilm of a wetting agent which will allow the lump ferro-silicon tobecome wet by molten slag, and adding the coated lump ferro-silicon tothe furnace bath, whereby the lump ferro-silicon immediately becomes wetby the slag and sinks through the slag and immediately goes intosolution at the inter-face between slag and metal, in an amountsuflicient to effectively deoxidize the upper layer of the metal and thelower layer of the slag in the region of the interface.

2. In the manufacture of iron and steel, the method of blocking the heatwhen it has reached the desired carbon content, which consists incoating one inch and larger lump dense 50% ferro-silicon with a film ofsodium nitrate which will allow the lump ferro-silicon to become wet bymolten slag, and adding the coated lump ferro-silicon to the furnacebath, whereby the lump ferro-silicon immediately becomes wet by the slagand sinks through the slag and immediately goes into solution at theinter-face between slag and metal, in an amount sufficient toeffectively deoxidize the upper layer of the metal and the lower layerof the slag in the region of the inter-face.

JAMES C. VIGNOS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,545,690 Petinot July 14, 19252,361,627 Herty Oct. 31, 1944 2,446,759 Griffiths Aug. 10, 1948 OTHERREFERENCES Basic Open Hearth Steel Making, (1944), pages -113, 230.

The Physical Chemistry of Steelmaking-Deoxidation with Silicon in theBasic Open Hearth Process (Cooperative Bulletin 38), page 7'7 (1930)

1. IN THE MANUFACTURE OF IRON AND STEEL, THE METHOD OF BLOCKING THE HEATWHEN IT HAS REACHED THE DESIRED CARBON CONTENT, WHICH CONSISTS INCOATING ONE INCH AND LARGER LUMP DENSE 50% FERRO-SILICON WITH THE FILMOF A WETTING AGENT WHICH WILL ALLOW THE LUMP FERRO-SILCON TO BECOME WETBY MOLTEN SLAG AND ADDING THE COATED LAMP FERRO-SILICON TO THE FURANCEBATH, WHEREBY THE LUMP FERRO-SILICON IMMEDIATELY BECOMES WET BY THE SLAGAND SINKS THROUGH THE SLAG AND IMMEDIATELY GOES INTO SOLUTION AT THEINTER-FACE BETWEEN SLAG AND METAL, IN AN AMOUNT SUFFICIENT TOEFFECTIVELY DEOXIDIZE THE UPPER LAYER OF THE METAL AND THE LOWER LAYEROF THE SLAG IN THE REGION OF THE INTERFACE.